Future emission regulations expected to be implemented in both in the United States and Europe will require the automotive emission system to work with high efficiency within a very short time after cold-starting of the engine, perhaps within 20 seconds. In the automotive industry, a number of approaches are under investigation to achieve rapid emissions control after cold-starting. One approach involves electrically heating the automotive catalyst during cold starting, another involves the use of hydrocarbon adsorption traps in the exhaust system, and yet another the use of exhaust gas burners to rapidly boost the temperature of the exhaust gas. Highly loaded palladium (Pd) containing three-way catalysts which are close coupled to the engine are still another approach to achieve fast light-off. The term "three-way" refers to catalysts that are able to simultaneously convert hydrocarbons, carbon monoxide and nitrogen oxides present in automotive exhaust gases to more desirable species. This last approach shows promise for use either in conjunction with, or in lieu of, the more complicated technologies noted above. This new generation of highly loaded Pd-containing catalysts demonstrates both improved durability and light-off characteristics when compared to conventional platinum/rhodium three-way catalysts.
We have unexpectedly found a novel method of preconditioning Pd-containing three-way catalysts which significantly lowers their light-off temperature during a subsequent cold-starting, as tested in synthetic gas mixtures resembling engine exhaust gases. When this preconditioning method is applied to non-palladium three-way catalysts like platinum, a similar improvement in light-off temperature is not seen.